The goal of this proposal is to study the function of somatic cells in regulating the asymmetric division of germline stem cells during oogenesis in Drosoplila. Asymmetric division of the germline stem cells gives rise to a daughter cell that remains undifferentiated, and another daughter cell that undergoes differentiation and develops into a mature oocyte. I propose to test the putative somatic effects on regulating germline stem cell asymmetric division by ablating specific enhancer trap induced LacZ expressing somatic cells adjacent to the germline stem cells using a photochemical inactivation method. I will also characterize, at the molecular level, a stem cell gene called ovarette (ovt) that phenotypically presents itself as a strong candidate for encoding a somatic factor involved in establishing the asymmetry of germ line stem cell division. Failure of the normal function of this gene results in two developmental anomalies: the proliferation of undifferentiated stem cells or the production of a limited number of egg chambers apparently without division. This suggests that under normal conditions, the ovt gene is involved in the somatic control of germline stem cell differentiation. I will analyze ovt DNA sequence and the pattern of transcription to